In the field of wireless and optical communication, an orthogonal frequency division multiplexing system (OFDM: Orthogonal Frequency Division Multiplexing) is proposed for multiplexing transmitted signals in the frequency domain (for example, refer to Non-Patent Document 1).
In OFDM, there is an advantage in that the sampling frequency of an analog to digital converter (ADC: Analog Digital Converter) for discretizing received signals can be set to a frequency lower than a frequency of twice the baud rate of the received signals. Therefore, for example in a wireless LAN (Local Area Network) applied to IEEE802.11a, it is known that a band of approximately 16.6 MHz in a signal band of 20 MHz (megahertz) is used for data signals.
On the other hand, in single carrier transmission, an ADC is required that can be adapted to a sampling frequency of approximately twice the frequency band of a signal. Therefore the advantage of being able to set a frequency lower than the frequency of twice the baud rate in OFDM is that signals can be transmitted efficiently by an ADC with a low sampling frequency, especially in optical communication in which the application is limited by the sampling frequency of the ADC and high frequency wireless communication.
Moreover, in OFDM, the higher the number of frequency channels is increased, the easier the setting of the guard interval becomes, so that it can be assumed that flat fading will occur in each of the frequency channels. As a result, in a practical wireless system, a frequency channel number of approximately 64 to 1024 is selected. Furthermore, in general, in an OFDM system, the frequency at a receiving device is “0”, that is, it has a frequency channel corresponding to a DC component. In a frequency channel corresponding to a DC component, the characteristics deteriorate due to the influence of interference between signals and noise. Therefore, frequency channels corresponding to these are not generally used.
In the fields of wireless communication and optical communication, a frequency division multiplexing system (FDM: Frequency Division Multiplexing) and an orthogonal frequency division multiplexing system (OFDM: Orthogonal Frequency Division Multiplexing) for multiplexing transmitted signals in the frequency domain are proposed. In communication systems in which signals are multiplexed in the frequency domain, on the receiving side, it is possible to extract and decode corresponding frequency domains using analog filters and Fourier transforms (for example, refer to Non-Patent Document 3).